This invention relates to a glow plug for a compression-ignition internal combustion engine having a swirl-producing precombustion chamber.
Diesel engines having a precombustion chamber to each engine cylinder generally utilize a glow plug to preheat air in the precombustion chamber in advance of fuel injection into the precombustion chamber at starting of the engine in a cold state, i.e. when the air can hardly be heated by compression to a temperature sufficient for reliable ignition of the injected fuel.
In many cases the precombustion chamber is formed as a swirl chamber to ignite fuel while air squeezed into the precombustion chamber is violently swirling thereby to attain efficient combustion in the main combustion chamber. To accomplish effective preheating of air in the swirl chamber at cold starting of the engine, the glow plug is screwed into an engine block such that a heater portion of the glow plug fully protrudes into the swirl chamber with its tip approximately in the middle of the swirl chamber.
The glow plug is utilized (energized) only at the start of the engine: at other times (during normal operation of the engine) the glow plug is kept unenergized. In other words, except at cold starting of the engine the glow plug is useless and because a nuisance to the function of the precombustion chamber. The heater portion of the glow plug offers an obstruction to the flow of air forced into the precombustion chamber and, furthermore, tends to cause weakening of the intensity of a swirl produced in the precombustion chamber. Failure in producing a sufficiently violent swirl of air in the swirl-producing precombustion chamber leads to an inefficient combustion in the main combustion chamber and will result in that the output of the engine remains on an insufficient level and that, particularly when exhaust gas recirculation is effected under high load operating conditions of the engine, the engine tends to emit black smoke.